Apparatus and method for transmitting/receiving the Hybrid-ARQ ACK/NACK signal in mobile communication system

ABSTRACT

An apparatus and method for transmitting/receiving a Hybrid Automatic Repeat reQuest (HARQ) Acknowledge/Negative acknowledge (ACK/NACK) signal in a mobile communication system. The apparatus and method distribute a CDM segment, to which an ACK/NACK signal is mapped, in the frequency domain of an OFDM symbol, and repeatedly transmits the CDM segment, thereby providing diversity gain in the time-frequency domain. Further, the apparatus and method provide a mapping rule for distributing transmit power between OFDM symbols to which the ACK/NACK signal is mapped and transmitted, thereby preventing a particular OFDM symbol power-overload, and thus contributing to improvement of the entire system performance.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to a KoreanPatent Application filed in the Korean Intellectual Property Office onAug. 21, 2007 and assigned Serial No. 2007-83876, a Korean PatentApplication filed in the Korean Intellectual Property Office on Sep. 13,2007 and assigned Serial No. 2007-93321, and a Korean Patent Applicationfiled in the Korean Intellectual Property Office on Jan. 14, 2008 andassigned Serial No. 2008-3910, the disclosures of all of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method fortransmitting and receiving an Acknowledge/Negative acknowledge(ACK/NACK) signal supporting Hybrid Automatic Repeat reQuest (HARQ) in amobile communication system.

2. Description of the Related Art

Currently, in mobile communication systems, intensive research is beingconducted on Orthogonal Frequency Division Multiple Access (OFDMA) orSingle Carrier—Frequency Division Multiple Access (SC-FDMA) as apotential scheme for high-speed data transmission on wireless channels.

3^(rd) Generation Partnership Project (3GPP), a standard group forasynchronous cellular mobile communication, is studying Long TermEvolution (LTE) or an Evolved Universal Terrestrial Radio Access(E-UTRA) system, which is the next-generation mobile communicationsystem, based on the above-stated multiple access scheme.

The multiple access scheme allocates and manages time-frequencyresources on which data or control information is transmitted for eachuser without overlapping each other, i.e., orthogonality is maintainedfor the time-frequency resources in order to distinguish data or controlinformation of each user. For a control channel, the multiple accessscheme can additionally allocate code resources for distinguishingcontrol information of each user.

FIG. 1 is a diagram illustrating a transmission structure on atime-frequency domain for data or control channels transmitted over aDownLink (DL) in an LTE system to which the present invention isapplied.

In FIG. 1, the vertical axis represents a time domain, and thehorizontal axis represents a frequency domain. The minimum transmissionunit in the time domain is an OFDM symbol. N_(symb) OFDM symbols 102 areincluded in one slot 106 and two slots are included in one subframe. Alength of the slot is 0.5 ms, and a length of the subframe is 1.0 ms.The minimum transmission unit in the frequency domain is a subcarrier,and the entire system transmission band includes a total of N_(BW)subcarriers 104.

In the time-frequency domain, the basic unit of wireless resources is aResource Element (RE) 112, which can be represented by an OFDM symbolindex and a subcarrier index. A Resource Block (RB) 108 is defined byN_(symb) consecutive OFDM symbols 102 in the time domain, and N_(RB)consecutive subcarriers 110 in the frequency domain. Therefore, one RB108 includes N_(symb)* N_(RB) REs 112. Generally, the minimumtransmission unit of data is the RB. In the current LTE system,N_(symb)=7, N_(RB)=12, and N_(BW) has a value that is proportional tothe system transmission band.

It is assumed that control information is transmitted within first NOFDM symbols in a subframe. Presently, a maximum of 3 is considered as avalue of N. Therefore, a value of N varies according to the amount ofcontrol information to be transmitted on a subframe.

The control information includes an indicator of the number of OFDMsymbols over which the control information is transmitted, UpLink (UL)or DL scheduling information, an ACK/NACK signal, and Multiple InputMultiple Output (MIMO)-related control information.

HARQ is an important technology used for increasing reliability and datathroughput of data transmission in a packet-based mobile communicationsystem. HARQ refers to a combined technology of an Automatic RepeatreQuest (ARQ) technology and a Forward Error Correction (FEC)technology.

ARQ refers to a technology in which a transmitter assigns sequencenumbers to data packets according to a predetermined scheme andtransmits the data packets. A receiver requests the transmitter toretransmit missing packet(s) among the received packets using thesequence numbers, thereby achieving reliable data transmission.

FEC refers to a technology for adding redundant bits to transmissiondata before transmission, such as the convolutional coding or turbocoding, to cope with an error occurring in the noise or fadingenvironment during the data transmission/reception process, therebydecoding the originally transmitted data.

In a system using HARQ, a receiver decodes received data through aninverse FEC process, and determines if the decoded data has an errorthrough Cyclic Redundancy Check (CRC) check. If there is no error, thereceiver feeds back an ACK to the transmitter, so that the transmittercan transmit the next data packet. However, if there is an error, thereceiver feeds back a NACK to the transmitter, thereby requestingretransmission of the previously transmitted packet. Through the aboveprocess, the receiver combines the previously transmitted packet withthe retransmitted packet, thereby obtaining energy gain and improvedreception performance.

FIG. 2 is a diagram illustrating an example of data transmission by HARQto which the present invention is applied.

Referring to FIG. 2, the horizontal axis represents the time domain.Reference numeral 201 represents an initial data transmission. A datachannel is a channel over which data is actually transmitted. Areceiver, receiving data transmission 201, attempts demodulation on thedata channel. In this process, if it is determined that the datatransmission fails in successful demodulation, the receiver feeds back aNACK 202 to a transmitter. Upon receipt of the NACK 202, the transmitterperforms retransmission on the initial transmission 201, i.e., a firstretransmission 203. Therefore, data channels in the initial transmission201 and the first retransmission 203 transmit the same information. Eventhough the data channels transmit the same information, they may havedifferent redundancies.

Upon receipt of the data transmission 203, the receiver performscombining on the retransmission 203 with the initial transmission 201data, and attempts demodulation of the data channel depending on thecombining result. If it is determined that the data transmission failsto successfully demodulate, the receiver feeds back a NACK 204 to thetransmitter. Upon receipt of the NACK 204, the transmitter performs asecond retransmission 205, a predetermined time period after the time ofthe first retransmission 203. Therefore, data channels for the initialtransmission 201, the first retransmission 203, and the secondretransmission 205 all transmit the same information.

Upon receiving data of the second retransmission 205, the receivercombines the initial transmission 201, the first retransmission 203, andthe second retransmission 205, and demodulates the data channel. If itis determined that the data transmission is successfully demodulated,the receiver feeds back an ACK 206 to the transmitter.

Upon receipt of the ACK 206, the transmitter performs another initialtransmission 207 on the next data. The initial transmission 207 can beimmediately performed when the ACK 206 is received, or can be performedafter a lapse of a certain time, depending on the scheduling result.

In order to support HARQ, the receiver should transmit an ACK/NACK, orfeedback information, to the transmitter. A channel used fortransmitting the ACK/NACK is called a Physical HARQ Indicator Channel(PHICH).

When such communication environments are taken into consideration, thereis a need for a detailed description as to how the system using HARQwill transmit an ACK/NACK signal in connection with data transmission.In particular, there is a need for a detailed scenario as to how anFDMA-based mobile communication system will transmit ACK/NACK signalsfor a plurality of users within first N OFDM symbols in a subframe,i.e., there is a demand for an ACK/NACK signal transmission andreception scheme in which HARQ is supported and orthogonality isguaranteed for a plurality of users in the time-frequency domain.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve the aboveand other problems occurring in the prior art, and the present inventionprovides an apparatus and method for transmitting and receiving anACK/NACK signal supporting Hybrid Automatic Repeat reQuest (HARQ) in amobile communication system.

Further, the present invention provides an apparatus and method formapping a plurality of HARQ ACK/NACK signals to at least one OFDM symbolbefore transmission and reception in a mobile communication system.

Further, the present invention provides an apparatus for distributingCDM segments for a plurality of ACK/NACK signals within OFDM symbols,before transmission and reception in a mobile communication system.

Further, the present invention provides a method for repeatedlytransmitting and receiving a plurality of ACK/NACK signals through atleast one OFDM symbol in a mobile communication system including atransmitter and a receiver.

Further, the present invention provides a method for transmitting andreceiving HARQ ACK/NACK signals through two OFDM symbols by varying amapping pattern based on the number of used antennas in a mobilecommunication system including a transmitter and a receiver.

Further, the present invention provides an HARQ ACK/NACK mapping methodfor repeatedly transmitting and receiving HARQ ACK/NACK signals throughtwo OFDM symbols, three times, in a mobile communication systemincluding a transmitter and a receiver.

In accordance with one aspect of the present invention, there isprovided a method for transmitting by a Node B an Acknowledge/Negativeacknowledge (ACK/NACK) signal to each User Equipment (UE) according tosuccess in demodulation of data received from each UE in a mobilecommunication system. The ACK/NACK signal transmission method includesdetermining the number of Orthogonal Frequency Division Multiplexing(OFDM) symbols for control information transmission of a subframe towhich an ACK/NACK signal, that the Node B currently desires to transmit,belongs; determining a size of a Code Division Multiplexing (CDM)segment according to the determined number of OFDM symbols so as tomaintain orthogonality between resource sets for ACK/NACK transmissionand between ACK/NACK signals of CDM segment sets in the resource setsfor ACK/NACK transmission; determining a location where mapping isperformed in a frequency domain so that frequency diversity gain ismaximized; generating an ACK/NACK signal according to presence/absenceof an error in the data received from the UE; spreading the ACK/NACKsignal and mapping the spread ACK/NACK signal to the CDM segment;repeating an ACK/NACK signal mapped to the CDM segment in the frequencydomain a predetermined number of times; mapping the repeated ACK/NACKsignal to the resource sets for ACK/NACK transmission; and transmittingthe mapped ACK/NACK signal to the UE.

In accordance with another aspect of the present invention, there isprovided a method for transmitting by a Node B an Acknowledge/Negativeacknowledge (ACK/NACK) signal to each User Equipment (UE) according tosuccess in demodulation of data received from each UE in a mobilecommunication system. The ACK/NACK signal reception method includesdetecting, by the UE, information on the number of Orthogonal FrequencyDivision Multiplexing (OFDM) symbols for control informationtransmission from a control channel format indicator included in asignal received from the Node B; determining a Code DivisionMultiplexing (CDM) segment set that the Node B used for ACK/NACK signaltransmission, among the predefined resource sets for ACK/NACKtransmission according to the detected number of OFDM symbols;extracting an ACK/NACK signal from each CDM segment to which theACK/NACK signal is mapped; despreading the extracted ACK/NACK signal;and combining and decoding the despread ACK/NACK signal.

In accordance with another aspect of the present invention, there isprovided an apparatus for transmitting an Acknowledge/Negativeacknowledge (ACK/NACK) signal to each User Equipment (UE) according tosuccess in demodulation of data received from each UE in a mobilecommunication system. The ACK/NACK signal transmission apparatusincludes a unitary transformer for transforming an ACK/NACK signal intoan orthogonal signal; a K-times repeater for K-times repeating theACK/NACK signal, transformed into the orthogonal signal by the unitarytransformer, in units of Code Division Multiplexing (CDM) segments; asubcarrier mapper for generating the ACK/NACK signal received from theK-times repeater according to the CDM segment; a multiplexer formultiplexing the ACK/NACK signal received from the subcarrier mapper toat least one of other control information, a pilot signal, and data; anInverse Fast Fourier Transformer (IFFT) for transforming the ACK/NACKsignal received from the multiplexer into a time-domain signal; aparallel-to-serial converter for converting an output signal of the IFFTinto a serial signal; a Cyclic Prefix (CP) inserter for inserting a CPfor prevention of inter-symbol interference into the ACK/NACK signalconverted into the serial signal; and an ACK/NACK controller fordetermining a size of the unitary transformer according to the maximumsize of a CDM segment for ACK/NACK transmission, determining arepetition of the K-times repeater and a spreading factor of thesubcarrier mapper so that frequency-domain diversity gain of theACK/NACK signal is maximized, and controlling the unitary transformer,the K-times repeater, and the subcarrier mapper depending on thedetermination.

In accordance with another aspect of the present invention, there isprovided an apparatus for transmitting an Acknowledge/Negativeacknowledge (ACK/NACK) signal to each User Equipment (UE) according tosuccess in demodulation of data received from each UE in a mobilecommunication system. The ACK/NACK signal reception apparatus includes aCyclic Prefix (CP) remover for removing a CP from a signal received fromthe Node B; a serial-to-parallel converter for converting the CP-removedsignal into a parallel signal; a Fast Fourier Transformer (FFT) fortransforming the parallel-converted signal into a frequency-domainsignal; an ACK/NACK symbol extractor for extracting an ACK/NACK symbolfrom the signal output from the FFT; a unitary de-transformer forreceiving the signal output from the ACK/NACK symbol extractor in unitsof Code Division Multiplexing (CDM) segments a predetermined number oftimes, and performing unitary de-transform thereon; a K-times combinerfor combining the signal output from the unitary de-transformer apredetermined number of times and outputting an ACK/NACK signal; and anACK/NACK controller for determining information indicating a number ofOFDM symbols the ACK/NACK signal is transmitted through, a repetitionlocation of the CDM segment, a size of the unitary de-transformer, and arepetition of the CDM segment, and controlling the ACK/NACK symbolextractor, the unitary de-transformer, and the K-times combiner.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a diagram illustrating time-frequency domain resources fordata or control channels in an LTE system to which the present inventionis applied;

FIG. 2 is a diagram illustrating a transmission process for data andACK/NACK signals based on HARQ to which the present invention isapplied;

FIG. 3 is a diagram illustrating a transmission structure for DLACK/NACK signals in an LTE system according to the present invention;

FIG. 4 is a diagram illustrating simulation results on an ACK/NACKsignal based on a repetition of CDM segments in an OFDM system;

FIG. 5 is a diagram illustrating a CDM segment mapping method forACK/NACK signal transmission according to a first embodiment of thepresent invention;

FIG. 6 is a diagram illustrating a transmission procedure for anACK/NACK signal in a Node B according to the first embodiment of thepresent invention;

FIG. 7 is a diagram illustrating a reception procedure for an ACK/NACKsignal in a UE according to the first embodiment of the presentinvention;

FIG. 8 is a diagram illustrating a structure of a transmission apparatusfor an ACK/NACK signal according to the present invention;

FIG. 9 is a diagram illustrating a structure of a reception apparatusfor an ACK/NACK signal according to the present invention;

FIG. 10 is a diagram illustrating a CDM segment mapping method forACK/NACK signal transmission according to a second embodiment of thepresent invention;

FIG. 11 is a diagram illustrating a CDM segment mapping method forACK/NACK signal transmission according to a third embodiment of thepresent invention;

FIG. 12 is a diagram illustrating a transmission procedure for anACK/NACK signal in a Node B according to the third embodiment of thepresent invention;

FIG. 13 is a diagram illustrating a reception procedure for an ACK/NACKsignal in a UE according to the third embodiment of the presentinvention;

FIG. 14 is a diagram illustrating an A-B-A antenna mapping pattern in anSFBC scheme in which SF=4 and 4 transmit antennas are used, according toa fourth embodiment of the present invention;

FIG. 15 is a diagram illustrating an B-A-B antenna mapping pattern in anSFBC scheme in which SF=4 and 4 transmit antennas are used, according tothe fourth embodiment of the present invention;

FIG. 16 is a diagram illustrating a method for mapping a PHICH group ina time-frequency domain in an SFBC scheme in which SF=4 and 4 transmitantennas are used, according to the fourth embodiment of the presentinvention;

FIG. 17 is a diagram illustrating an A′-B′-A′ antenna mapping pattern inan SFBC scheme in which SF=2 and 4 transmit antennas are used, accordingto a fifth embodiment of the present invention;

FIG. 18 is a diagram illustrating an B′-A′-B′ antenna mapping pattern inan SFBC scheme in which SF=2 and 4 transmit antennas are used, accordingto a fifth embodiment of the present invention;

FIG. 19 is a diagram illustrating a method for mapping a PHICH group ina time-frequency domain in an SFBC scheme in which SF=2 and 4 transmitantennas are used, according to the fifth embodiment of the presentinvention; and

FIG. 20 is a diagram illustrating a method for mapping a PHICH group ina time-frequency domain in an SFBC scheme in which SF=4 and 4 transmitantennas are used, according to a sixth embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the annexed drawings. In the followingdescription, a detailed description of known functions andconfigurations incorporated herein has been omitted for clarity andconciseness. Terms used herein are defined based on functions in thepresent invention and may vary according to users, operator intention,or usual practices. Therefore, the definition of the terms should bemade based on contents throughout the specification.

A description will now be made of a transmission/reception operation ofa Node B (or Base Station) and a User Equipment ((UE) or Mobile Station)for transmitting control information, specifically, ACK/NACK signalssupporting HARQ, in an FDMA-based mobile communication system.

FIG. 3 is a diagram illustrating a transmission structure for DLACK/NACK signals in a current LTE system to which the present inventionis applied.

Referring to FIG. 3, the LTE system uses the time-frequency resourcesand also code resources in order to distinguish an ACK/NACK signal ofeach user. The ACK/NACK signal, 1-bit of information, notifies an ACK orNACK. When the ACK/NACK signal is spread, ‘number of bits of ACK/NACKsignal’* ‘spreading factor (SF)’ chips are generated, and beforetransmission, the generated chips are mapped to Code DivisionMultiplexing (CDM) segments for ACK/NACK transmission.

The CDM segment, a resource unit including consecutive REs in thetime-frequency domain, is characterized in that it is robust againstinterference signals and restricts performance degradation of orthogonalcodes due to the frequency-selective characteristic of wirelesschannels. In addition, for reception performance improvement throughadditional diversity gain, the CDM segment is repeatedly transmitted onthe frequency domain a predetermined number of times. A repetition(number of repetitions) for the CDM segment is determined considering adesired diversity gain and wireless resource overhead.

A size of one CDM segment is equal to a size of the generated chip, andthe number of ACK/NACK signals to which the CDM segment can bemultiplexed is equal to the SF. The above transmission scheme is calleda “hybrid FDM/CDM scheme”.

The number of OFDM symbols, to which the ACK/NACK signal is mapped andtransmitted, as described above, cannot exceed first N OFDM symbols in asubframe on which control information is transmitted. In this context,for a value of N, 1 or 3 is now considered.

For N=1, when a user is located a shorter distance from a Node B, it issufficient to satisfy predefined reception reliability of an ACK/NACKsignal even though the ACK/NACK signal is transmitted over one OFDMsymbol. On the other hand, when a user is located a longer distance fromthe Node B, it is insufficient for a transmission interval of anACK/NACK signal to satisfy the predefined reception reliability onlywith one OFDM symbol (N=1), and the ACK/NACK signal is transmitted overthree OFDM symbols (N=3).

It is assumed in FIG. 3 that an ACK/NACK signal for each user istransmitted within the first OFDM symbol in the subframe, i.e., usingthe same frequency resource, for N=1. In this case, ACK/NACK signals for4 users are spread with a spreading factor 4 (SF=4) corresponding to thenumber of ACK/NACK signals mapped to the CDM segments, use the sametime-frequency resources, and are distinguished using different length-4orthogonal codes.

That is, in the example of FIG. 3, an ACK/NACK signal #1 for user #1, anACK/NACK signal #2 for user #2, an ACK/NACK signal #3 for user #3, andan ACK/NACK signal #4 for user #4 are spread with different SF=4orthogonal codes, and then repeatedly mapped to 4 CDM segments 320, 322,324, and 326 before transmission. Similarly, an ACK/NACK signal #5 foruser #5, an ACK/NACK signal #6 for user #6, and an ACK/NACK signal #7for user #7, and an ACK/NACK signal #8 for user #8 are spread withdifferent SF=4 orthogonal codes, and then repeatedly mapped to 4 CDMsegments 328, 330, 332, and 334 before transmission. Here, the CDMsegments are made such that pilot signals (also known as ReferenceSignal (RS)) for channel estimation should not overlap with othercontrol signals except for ACK/NACK.

In the exemplary case of FIG. 3, CDM segments are created with thelocation of additional pilot signals 315 for a system operating aplurality of transmit antennas taken into consideration. The repeatedCDM segments 316 and 318 are equal in size.

As to an interval between the CDM segments, which are repeatedlytransmitted on the frequency domain a predetermined number of times, theCDM segments should be created such that they are spaced as far fromeach other as possible, in order to maximize frequency diversity.Therefore, when a transmission interval of an ACK/NACK signal cannotsatisfy a predefined reception reliability of the ACK/NACK signal onlywith one OFDM symbol because a user is located a longer distance from aNode B, because the ACK/NACK signal should be dispersedly transmittedover a 3-OFDM symbol interval, there is a need for a detailed definitionof a method for mapping CDM segments to OFDM symbols. Accordingly, thepresent invention provides a detailed method for mapping CDM segmentsfor ACK/NACK signals to at least one OFDM symbol. In addition, thepresent invention provides a rule based for distributing andtransmitting ACK/NACK signals for a plurality of users for an availableOFDM symbol interval.

FIG. 4 is a diagram illustrating simulation results based on arepetition of CDM segments when an OFDM system transmits ACK/NACKsignals using one transmit antenna.

This simulation shows a received bit energy-to-noise ratio E_(b)/N₀versus a Bit Error Rate (BER) when a length of orthogonal codes is 4 anda repetition is 1, 2, 3, 4, 8, and 24, in a fading channel environmentwhere a user moves, for example, at 3 km/h. As a whole, it is shown thatan increase in repetition contributes to performance improvement where avalue of E_(b)/N₀ necessary for obtaining the same BER is reduced, andan increase in repetition reduces the performance improvement.Therefore, given the BER performance and the limited resources, it ispreferable to repeat the CDM segments four times, for system design.

The number of first N OFDM symbols in a subframe on which controlinformation is transmitted varies according to the amount of desiredtransmission control information at every subframe. The controlinformation includes a Control Channel Format Indicator (CCFI)indicating the number of OFDM symbols over which control information istransmitted, UL/DL scheduling information, ACK/NACK signal, etc. TheCCFI is transmitted in the first OFDM symbol to notify a transmissioninterval N of control information. UL/DL scheduling informationdisperses the control information over the notified-N OFDM symbols toobtain a diversity effect. In the current LTE system, a maximum of 3 canapply as a value of the transmission interval N, and the possible numberof OFDM symbols to which the ACK/NACK signals are mapped and transmittedis 1 or 3, as described above.

The present invention provides a detailed method for mapping CDMsegments to OFDM symbols when dispersedly transmitting ACK/NACK signalsfor a 3-OFDM symbol interval.

Further, the present invention defines a mapping method such that powerbetween OFDM symbols to which ACK/NACK signals are mapped is uniformlydispersed, if possible, thereby preventing the situation where aparticular OFDM symbol is overloaded. That is, at an arbitrary instant,the maximum transmit power of a Node B should be maintained below apredetermined value due to the restriction of a Node B power amplifier,and the Node B should consider the above matters even when mapping CDMsegments for transmitting ACK/NACK signals to OFDM symbols.

CCFI, which is an indicator indicating the number of OFDM symbols overwhich control information is transmitted, is always mapped to the firstOFDM symbol in the subframe during its transmission, and because theCCFI requires a higher reception reliability, its transmit power isgenerally relatively high. Therefore, ACK/NACK CDM segments for ACK/NACKsignal transmission are created such that, if possible, they are lessfrequently mapped to the OFDM symbol to which the CCFI is mapped andtransmitted, thereby preventing the first OFDM symbol to be overloaded.

First Embodiment

A first embodiment of the present invention considers a situation inwhich an ACK/NACK signal is spread with a spreading factor 4 and mappedto a CDM segment, the CDM segment is repeated 4 times, and the ACK/NACKsignal is transmitted during the first 1 or 3 OFDM symbols in asubframe.

FIG. 5 is a diagram illustrating a CDM segment mapping method forACK/NACK signal transmission according to a first embodiment of thepresent invention. For convenience, only CCFIs and ACK/NACK signals areshown. Other UL/DL scheduling information and pilot signals (or RSs) arenot shown.

Referring to FIG. 5, reference numeral 506 identifies where the CCFI ismapped to the first OFDM symbol, and repeatedly transmitted in thefrequency domain in order to obtain additional diversity gain. In thecase where according to the simulation results of FIG. 4, CDM segmentsare repeated 4 times, and mapped to the first 3 OFDM symbols in onesubframe, the method divides resources for ACK/NACK transmission intotwo types: set #1 and set #2. Herein, a set of CDM segments that arerepeated 4-times is called a “CDM segment set”, and the CDM segment setis an element included in a resource set #1 for ACK/NACK transmission ora resource set #2 for ACK/NACK transmission.

The resource set #1 for ACK/NACK transmission represents resources forACK/NACK transmission, provided for once mapping a CDM segment to whichan ACK/NACK signal, intended to be transmitted to a particular UE, ismapped after being spread, to the first OFDM symbol for ACK/NACK signaltransmission (508), once mapping the CDM segment to the second OFDMsymbol for ACK/NACK signal transmission (514), and twice mapping the CDMsegment to the third OFDM symbol for ACK/NACK signal transmission (518and 522).

The resource set #2 for ACK/NACK transmission represents resources forACK/NACK transmission, provided for once mapping a CDM segment to whichan ACK/NACK signal, intended to be transmitted to another UE, is mappedafter being spread, to the first OFDM symbol for ACK/NACK signaltransmission (512), twice mapping the CDM segment to the second OFDMsymbol for ACK/NACK signal transmission (516 and 524), and once mappingthe CDM segment to the third OFDM symbol for ACK/NACK signaltransmission (520).

The ACK/NACK CDM segments mapped to each OFDM symbol in each set arecreated such that they do not overlap each other in the frequencydomain, thereby maximally obtaining a frequency diversity effect.Different frequencies can be used for ACK/NACK signal multiplexingbetween the resource set #1 for ACK/NACK transmission and the resourceset #2 for ACK/NACK transmission.

Because one CDM segment set can distinguish a maximum of 4 ACK/NACKsignals by orthogonal codes, a plurality of CDM segment sets are definedand managed in order to multiplex a plurality of ACK/NACK signals. Theplurality of CDM segment sets are defined such that they are uniformlydistributed and included in each of the resource sets for ACK/NACKtransmission.

As the CDM segment sets are uniformly distributed to each of theresource sets for ACK/NACK transmission, information indicating whichresource set for ACK/NACK transmission and CDM segment set the UE shouldmonitor in order to receive the ACK/NACK signal from a Node B isimplicitly notified by a mapping relation with scheduling controlinformation without separate signaling, or notified by separate physicallayer or upper layer signaling.

FIG. 6 is a diagram illustrating a transmission procedure for anACK/NACK signal in a Node B according to the first embodiment of thepresent invention.

Referring to FIG. 6, in step 602, a Node B determines the number N ofOFDM symbols for control information transmission of a subframe to whichthe currently desired transmission ACK/NACK signal belongs, in order totransmit the ACK/NACK signal. A value of N is proportional to the amountof control information that the Node B desires to transmit in asubframe.

In step 604, the Node B determines if the number N of OFDM symbols isequal to 3.

If the number of OFDM symbols is 3, in step 606, the Node B determines asize of a CDM segment, a predefined resource set for ACK/NACKtransmission, and a CDM segment set in the resource set for ACK/NACKtransmission, as resources for ACK/NACK transmission. The size of theCDM segments is a value for maintaining orthogonality between ACK/NACKsignals multiplexed to CDM segments, and a fixed value is generallyused. In addition, the CDM segments are created such that they do notoverlap each other in the frequency domain, thereby maximally obtainingfrequency diversity gain. Further, the Node B determines resources forACK/NACK transmission such that power overload may not occur in aparticular OFDM symbol among the OFDM symbols for ACK/NACK transmission.The determined resources for ACK/NACK transmission are implicitlynotified to a UE in association with transmission resources to whichscheduling information transmitted together with ACK/NACK is mapped, ornotified to a UE through separate physical layer or upper layersignaling.

In step 608, the Node B generates an ACK/NACK signal according to thepresence or absence of an error in the data received from a UE, spreadsthe generated ACK/NACK signal, maps it to a CDM segment, and thenrepeatedly transmits the CDM segment four times in the frequency domainin order to obtain frequency-domain diversity gain. The 4-times repeatedCDM segments are mapped to the ACK/NACK signal transmission resourcesdetermined in step 606.

However, if it is determined in step 604 that the number of OFDM symbolsis not 3, in step 610, the Node B determines a size of a CDM segment anda location where the CDM segment is mapped in the frequency domain, asresources for ACK/NACK transmission.

In step 612, the Node B generates an ACK/NACK signal according to thepresence or absence of an error in the data received from a UE, spreadsthe generated ACK/NACK signal, maps it to a CDM segment, and thenrepeatedly transmits the CDM segment four times in the frequency domainin order to obtain frequency-domain diversity gain. The 4-times repeatedCDM segments are mapped to the resources for ACK/NACK transmissiondetermined in step 610.

FIG. 7 is a diagram illustrating a reception procedure for an ACK/NACKsignal in a UE according to the first embodiment of the presentinvention. The reception procedure in a UE corresponds to an inverseprocess of the Node B transmission procedure illustrated in FIG. 6.

Referring to FIG. 7, in step 702, a UE recognizes the number N of OFDMsymbols for control information transmission by a Node B, or itsequivalent information, through signaling. The information can beacquired through CCFI information transmitted from the Node B.

In step 704, the UE determines if the number N of OFDM symbols is equalto 3.

If it is determined in step 704 that the number of OFDM symbols is 3, instep 706 the UE determines with which CDM segment set the Node B hastransmitted an ACK/NACK signal, among the resource sets for ACK/NACKtransmission, defined for N=3.

The UE can determine the CDM segment by detecting the transmissionresources of the scheduling control information received together withan ACK/NACK signal, or signaling made through a physical layer and/orupper layer.

In step 708, the UE extracts an ACK/NACK signal from each CDM segment towhich the ACK/NACK signal is mapped, despreads it, combines the despreadACK/NACK signal with a signal despread after being extracted from eachCDM segment, and performs decoding thereon.

However, if it is determined in step 704 that a value of N is not 3, instep 710, the UE determines with which CDM segment set the Node B hastransmitted an ACK/NACK signal, among the resource sets for ACK/NACKtransmission, defined for N≠3. The UE can determine the CDM segment bydetecting the transmission resources of the scheduling controlinformation received together with an ACK/NACK signal, or signaling madethrough a physical layer and/or upper layer. In step 712, the UEextracts an ACK/NACK signal from each CDM segment to which the ACK/NACKsignal is mapped, despreads it, combines the despread ACK/NACK signalwith a signal despread after being extracted from each CDM segment, andperforms decoding thereon.

FIG. 8 is a diagram illustrating a structure of a transmission apparatusfor an ACK/NACK signal according to an embodiment of the presentinvention.

Referring to FIG. 8, a value of an ACK/NACK signal 801 is determinedaccording to whether demodulation of the data a Node B received fromeach UE is successful, or retransmission is required due to failure inthe demodulation. The ACK/NACK signal 801 is input to a unitarytransformer 802 where it is transformed into an orthogonal signal. AnACK/NACK controller 810 determines a size of the unitary transformer802, a repetition K in the frequency domain, and a repetition location,and controls the unitary transformer 802, a K-times repeater 803, and asubcarrier mapper 804. The size of the unitary transformer 802 is equalto a size of the CDM segment for ACK/NACK transmission, and isdetermined as a spreading factor having a predetermined size so as tomaintain orthogonality between ACK/NACK signals multiplexed in the CDMsegment for ACK/NACK transmission. Therefore, the unitary transformer802 receives as many ACK/NACK signals as the maximum size of the CDMsegment for ACK/NACK transmission, and transforms them into orthogonalsignals. The transformed output signals constitute a CDM segment of theACK/NACK signals. For example, the unitary transformer 802 can use aWalsh transform or a Discrete Fourier Transform (DFT) as a transformoperation for maintaining orthogonality between input signals.

The K-times repeater 803 K-times repeats the ACK/NACK signal, which istransformed into an orthogonal signal by the unitary transformer 802, inunits of CDM segments in order to acquire frequency domain diversity.The repetition is adjusted by the ACK/NACK controller 810, and it ispreviously defined between a Node B and a UE, or recognized in commonthrough signaling. The first embodiment of the present invention isdescribed for K=4 as an example.

The subcarrier mapper 804 generates the input signal received from theK-times repeater 803 according to the CDM segment. The K-times repeatedlocation is adjusted by the ACK/NACK controller 810, and it isdetermined according to the number of OFDM symbols for ACK/NACKtransmission. The number of OFDM symbols is determined according to theamount of desired transmission control information and the channel stateof a UE that intends to receive an ACK/NACK signal, or to the UElocation in the cell. If the number of OFDM symbols for ACK/NACKtransmission is determined as 3, the Node B determines resources forACK/NACK transmission such that power overload may not occur in aparticular OFDM symbol among the OFDM symbols for ACK/NACK transmission.

As illustrated in FIG. 5, the first preferred embodiment of the presentinvention defines resource sets for ACK/NACK transmission as a set #1and a set #2, so that ACK/NACK signals for individual UEs should beuniformly distributed on the resource sets for ACK/NACK transmission.The resource set #1 for ACK/NACK transmission has a property that a CDMsegment is once mapped to the first OFDM symbol, once mapped to thesecond OFDM symbol, and twice mapped to the third OFDM symbol. Theresource set #2 for ACK/NACK transmission has a property that CDMsegment is once mapped to the first OFDM symbol, twice mapped to thesecond OFDM symbol, and once mapped to the third OFDM symbol.

If the number of OFDM symbols for ACK/NACK transmission is determined as1, the Node B repeatedly maps the CDM segment four times to the firstOFDM symbol in a subframe on which the ACK/NACK signal is transmitted.

A multiplexer 805 multiplexes the ACK/NACK signal with other controlinformation, a pilot signal, and data. The multiplexed signal is thentransformed into a time-domain signal by Inverse Fast Fourier Transform(IFFT) 806. An output signal of the IFFT 806 is converted into a serialsignal in a parallel-to-serial converter 807. Thereafter, a CyclicPrefix (CP) for prevention of inter-symbol interference is added to theserial signal in a CP inserter 808, and then the signal is transmitted.

FIG. 9 is a diagram illustrating a structure of a reception apparatusfor an ACK/NACK signal according to a preferred embodiment of thepresent invention.

Referring to FIG. 9, in a UE, a CP remover 901 removes a CP from areceived signal from a Node B, and a serial-to-parallel converter 902converts the CP-removed signal into a parallel signal. The parallelsignal is transformed into a frequency-domain signal by a Fast FourierTransform (FFT) block 903. An ACK/NACK symbol extractor 904 extracts anACK/NACK symbol from the location of the time-frequency resources towhich the ACK/NACK symbol is mapped in the frequency-domain signaloutput from the FFT 903. The location of time-frequency resources towhich the ACK/NACK symbol is mapped is acquired by an ACK/NACKcontroller 907.

A unitary de-transformer 905 K times receives an output signalcorresponding to a CDM segment from the ACK/NACK symbol extractor 904 inunits of CDM segments, and performs unitary de-transform thereon. AK-times combiner 906 performs K-times combining on the output of theunitary de-transformer 905.

The ACK/NACK controller 907 determines information indicating the numberof OFDM symbols over which an ACK/NACK signal is transmitted, arepetition location of the CDM segment, a size of the unitaryde-transformer 905, and a repetition K of the CDM segment, and controlsthe ACK/NACK symbol extractor 904, the unitary de-transformer 905, andthe K-times combiner 906 depending thereon. Therefore, the UE finallyacquires an ACK/NACK signal from the combined signal.

Second Embodiment

A second embodiment of the present invention considers where an ACK/NACKsignal is spread with a spreading factor 4 and mapped to a CDM segment,the CDM segment is repeated 3 times, and the ACK/NACK signal istransmitted during first 2 OFDM symbols in a subframe.

FIG. 10 is a diagram illustrating a CDM segment mapping method forACK/NACK signal transmission according to the second embodiment of thepresent invention. As described above for FIG. 5, only CCFIs andACK/NACK signals are illustrated in FIG. 10, for convenience. OtherUL/DL scheduling information and pilot signals are not shown.

Referring to FIG. 10, reference numeral 1006 represents where the CCFIis mapped to the first OFDM symbol, and repeatedly transmitted in thefrequency domain in order to obtain additional diversity gain. When CDMsegments are repeated 3 times, and mapped to first 2 OFDM symbols in onesubframe, the proposed method maps CDM segments for ACK/NACKtransmission as will be described below. That is, the method once maps aCDM segment to which an ACK/NACK signal, intended to be transmitted to aparticular UE, is mapped after being spread, to the first OFDM symbolfor ACK/NACK signal transmission (1008), and twice maps the CDM segmentto the second OFDM symbol for ACK/NACK signal transmission (1014 and1018). The ACK/NACK CDM segments mapped to each OFDM symbol are createdsuch that they do not overlap each other in the frequency domain,thereby maximally obtaining a frequency diversity effect.

In the present embodiment, a set of the 3-times repeated CDM segments iscalled a “CDM segment set”. In the above example, because one CDMsegment set can distinguish a maximum of 4 ACK/NACK signals by length-4orthogonal codes, a plurality of CDM segment sets are defined andmanaged in order to multiplex a plurality of ACK/NACK signals. In thiscase, the multiple CDM segment sets are defined such that they do notoverlap each other in the frequency domain. In the example illustratedin FIG. 10, a CDM segment set including reference numerals 1012, 1016,and 1020 is additionally defined and managed.

As the CDM segment sets are uniformly distributed to each of theresource sets for ACK/NACK transmission, information indicating whichACK/NACK CDM segment set the UE should monitor in order to receive theACK/NACK signal from a Node B is implicitly notified by a mappingrelation with scheduling control information without separate signaling,or notified by separate physical layer or upper layer signaling.

A detailed transmission/reception apparatus of the second embodiment isequal to that of the first embodiment, so a description thereof will beomitted. However, the detailed parameters follow the assumptions made inthe second embodiment.

Third Embodiment

A third embodiment of the present invention, an example where thepresent invention is applied to MBMS Single Frequency Network (MBSFN)service supporting broadcast service such as Mobile-TV, generates onesubframe with 12 OFDM symbols and transmits an ACK/NACK signal duringfirst 2 OFDM symbols in one subframe.

The third embodiment, like the second embodiment, considers thesituation where an ACK/NACK signal is spread with a spreading factor 4and mapped to CDM segments, the CDM segment is repeated 3 times; and theACK/NACK signal is transmitted during first 2 OFDM symbols in asubframe. Particularly, as MBSFN fixes a transmission interval ofcontrol information including an ACK/NACK signal to first 2 OFDM symbolsin one subframe, there is no need for separate CCFI for indicating thecontrol information transmission interval. The third embodiment of thepresent invention, described below, can be usefully applied to MBSFNwhere CCFI is not needed.

FIG. 11 is a diagram illustrating a CDM segment mapping method forACK/NACK signal transmission according to the third embodiment of thepresent invention. For convenience, only ACK/NACK signals are shown, andother UL/DL scheduling information and pilot signals are not shown.

Referring to FIG. 11, when a CDM segment is repeated 3 times and mappedto first 2 OFDM symbols in one subframe, the method maps and operates aCDM segment for ACK/NACK transmission as will be described below. Themethod divides resources for ACK/NACK transmission into two types: set#1 and set #2. A set of the 3-times repeated CDM segments is called a“CDM segment set”, and the CDM segment set is an element included in aresource set #1 for ACK/NACK transmission or a resource set #2 forACK/NACK transmission.

As illustrated in FIG. 11, the resource set #1 for ACK/NACK transmissionrepresents resources for ACK/NACK transmission, provided for oncemapping a CDM segment to which an ACK/NACK signal, intended to betransmitted to a particular UE, is mapped after being spread, to thefirst OFDM symbol for ACK/NACK signal transmission (1108), and twicemapping the CDM segment to the second OFDM symbol for ACK/NACK signaltransmission (1114 and 1118).

The resource set #2 for ACK/NACK transmission represents resources forACK/NACK transmission, provided for twice mapping a CDM segment to whichan ACK/NACK signal, intended to be transmitted to another UE, is mappedafter being spread, to the first OFDM symbol for ACK/NACK signaltransmission (1112 and 1116), and once mapping the CDM segment to thesecond OFDM symbol for ACK/NACK signal transmission (1120).

The ACK/NACK CDM segments mapped to each OFDM symbol in each set aremade such that they do not overlap each other in the frequency domain,thereby maximally obtaining a frequency diversity effect. Differentfrequencies can be used for ACK/NACK signal multiplexing between theresource set #1 for ACK/NACK transmission and the resource set #2 forACK/NACK transmission.

In the third embodiment, because one CDM segment set can distinguish amaximum of 4 ACK/NACK signals by orthogonal codes, a plurality of CDMsegment sets are defined and managed in order to multiplex a pluralityof ACK/NACK signals. In this case, the plurality of CDM segment sets aredefined such that they are uniformly distributed and included in each ofthe resource sets for ACK/NACK transmission.

If a physical channel for transmitting ACK/NACK for an arbitrary UE(i)is defined as a Physical HARQ Indicator channel PHICH(i), the followingmapping method can determine which resource set for ACK/NACKtransmission the PHICH(i) uses.

Method 1

For i=odd number; PHICH(i)→resource set #1 for ACK/NACK transmission

For i=even number; PHICH(i)→resource set #2 for ACK/NACK transmission

Method 2

For floor(i/SF)=odd number; PHICH(i)→resource set #1 for ACK/NACKtransmission

For floor(i/SF)=even number; PHICH(i)→resource set #2 for ACK/NACKtransmission

More specifically, in Method 1, if an index i for a UE is an odd number,PHICH(i) transmits ACK/NACK using the resource set #1 for ACK/NACKtransmission, and if an index i for a UE is an even number, PHICH(i)transmits ACK/NACK using the resource set #2 for ACK/NACK transmission.Of course, the opposite mapping relation can also be defined.

In Method 2, if floor(i/SF) is an odd number, PHICH(i) transmitsACK/NACK using the resource set #1 for ACK/NACK transmission, and iffloor(i/SF) is an even number, PHICH(i) transmits ACK/NACK using theresource set #2 for ACK/NACK transmission. Of course, the oppositemapping relation can also be defined. In Method 2, SF indicates aspreading factor used for ACK/NACK transmission, and floor(a) is themaximum integer not greater than a.

Generally, a maximum of SF ACK/NACK signals can be multiplexed for oneCDM segment, and if transmission signals for ACK/NACK are mapped to atwo-dimensional region of I-channel and Q-channel, the multiplexingcapacity increases double. In this case, therefore, equation of Method 2is modified as floor(i/(SF*2)).

When a Node B intends to transmit ACK/NACK signals greater in number,both the two methods prevent overload of power or wireless resourcesfrom occurring in a particular OFDM symbol among the OFDM symbols forACK/NACK signal transmission.

Information indicating which resource set and CDM segment set forACK/NACK transmission the UE should monitor in order to receive theACK/NACK signal from a Node B is implicitly notified by a mappingrelation with scheduling control information without separate signaling,or notified by separate physical layer or upper layer signaling.

Defining the above operation makes it possible that power between OFDMsymbols, to which ACK/NACK signals are mapped, is uniformly dispersed ifpossible, thereby preventing the situation where a particular OFDMsymbol is power-overloaded. In addition, the definition makes itpossible that wireless resources for ACK/NACK transmission are uniformlydispersed over OFDM symbols, to which ACK/NACK signals are mapped, ifpossible, thereby preventing the situation where wireless resources of aparticular OFDM symbol are overloaded.

As described above, the CDM segments for ACK/NACK signals of each setare mapped such that they do not overlap in the frequency domain duringan OFDM symbol interval. That is, CDM segments for ACK/NACK signals,classified into at least 2 sets, are repeatedly transmitted apredetermined number of times, and are allocated during 2 OFDM symbolssuch that the total number of repeated CDM segments for ACK/NACK signalsof each set has the same ratio.

According to an example of the present invention, if the number of OFDMsymbols is 2 or a multiple of 2, and a repetition of CDM segments inACK/NACK signal group of each set is 3, ACK/NACK signals for UEsassociated with the set #1 are distributed and mapped in differentfrequency domains in a ratio of 2:1 between the first OFDM symbol andthe second OFDM symbol. Further, ACK/NACK signals for UEs associatedwith the set #2 are mapped such that they are distributed in thefrequency domains in a ratio of 1:2 between the first OFDM symbol andthe second OFDM symbol. Of course, the opposite mapping relation canalso be defined.

Therefore, CDM segments of set #1 and set #2 are mapped such that theyhave the same ratio in two OFDM symbols in terms of summation ofrepetitions. The CDM segments for ACK/NACK signals of the same set aredistributed and mapped so as to have the same frequency band interval inthe same OFDM symbol if possible. Therefore, ACK/NACK CDM segmentsmapped to OFDM symbols are defined such that they do not overlap eachother in the frequency domain, thereby providing frequency diversitygain.

FIG. 12 is a diagram illustrating a transmission procedure for anACK/NACK signal in a Node B according to the third embodiment of thepresent invention.

Referring to FIG. 12, in step 1202, a Node B determines the number N ofOFDM symbols for ACK/NACK signal transmission of a subframe to which thecurrently desired transmission ACK/NACK signal belongs, in order totransmit the ACK/NACK signal. A value of N is fixed to N=2 in a subframesupporting an MBSFN service, and is determined as N=1 or N=3 inproportion to the amount of desired transmission control information ina subframe not supporting the MBSFN service.

In step 1204, the Node B determines if the number N of OFDM symbols forACK/NACK signal transmission is equal to 2.

If it is determined in step 1204 that the number of OFDM symbols is 2,in step 1206, the Node B determines a size of a CDM segment, apredefined resource set for ACK/NACK transmission, and a CDM segment setin the resource set for ACK/NACK transmission, as resources for ACK/NACKtransmission. The size of the CDM segment is a value for maintainingorthogonality between ACK/NACK signals multiplexed to CDM segments, anda fixed value is generally used. In addition, the CDM segments are madesuch that they do not overlap each other in the frequency domain,thereby maximally obtaining frequency diversity gain. Further, the NodeB determines resources for ACK/NACK transmission such that poweroverload may not occur in a particular OFDM symbol among the OFDMsymbols for ACK/NACK transmission. That is, the desired transmissionACK/NACK signals are uniformly distributed and mapped to the resourceset #1 for ACK/NACK transmission and the resource set #2 for ACK/NACKtransmission.

The determined resources for ACK/NACK transmission are implicitlynotified to a UE in association with transmission resources to whichscheduling information transmitted together with ACK/NACK is mapped, ornotified to a UE through separate physical layer or upper layersignaling.

In step 1208, the Node B generates an ACK/NACK signal according to thepresence or absence of an error in the data received from a UE, spreadsthe generated ACK/NACK signal, maps it to a CDM segment, and thenrepeatedly transmits the CDM segment 3 times in the frequency domain inorder to obtain frequency-domain diversity gain. The 3-times repeatedCDM segments are mapped to the ACK/NACK signal transmission resourcesdetermined in step 1206.

The resource set #1 for ACK/NACK transmission once maps a CDM segment tothe first OFDM symbol, and twice maps the CDM segment to the second OFDMsymbol. The resource set #2 for ACK/NACK transmission twice maps a CDMsegment to the first OFDM symbol, and once maps the CDM segment to thesecond OFDM symbol. Therefore, the resource set #1 for ACK/NACKtransmission and the resource set #2 for ACK/NACK transmission are eachtransmitted through 2 OFDM symbols, satisfying the repetition=3.Accordingly, the resource set #1 and set #2 for ACK/NACK transmissionare transmitted through 2 OFDM symbols in the same ratio, guaranteeingdiversity gain and reception performance by 3-times repeatedtransmission through distributed transmission on the different frequencydomains and time domains. The CDM segments for a particular resource setfor particular ACK/NACK transmission are distributed and mapped havingthe same frequency interval if possible.

If it is determined in step 1204 that the number of OFDM symbols is not2, in step 1210, the Node B determines a size of a CDM segment and alocation where the CDM segment is mapped in the frequency domain, asresources for ACK/NACK transmission. If the number of OFDM symbols forACK/NACK transmission is 1, the Node B repeatedly maps an ACK/NACK CDMsegment to the first OFDM symbol in a subframe three times.

If the number of OFDM symbols for ACK/NACK transmission is 3, the Node Bonce maps the ACK/NACK CDM segment to each of the first OFDM symbol, thesecond OFDM symbol and the third OFDM symbol in the subframe, repeatingthe ACK/NACK CDM segment a total of 3 times.

In step 1212, the Node B generates an ACK/NACK signal according to thepresence or absence of an error in the data received from a UE, spreadsthe generated ACK/NACK signal, and transmits the spread signal to areceiver.

FIG. 13 is a diagram illustrating a reception procedure for an ACK/NACKsignal in a UE according to the third embodiment of the presentinvention. The reception procedure in a UE corresponds to an inverseprocess of the Node B transmission procedure illustrated in FIG. 12.

Referring to FIG. 13, in step 1302, a UE recognizes the number N of OFDMsymbols for control information transmission by a Node B, or itsequivalent information. The information can be acquired through separatesignaling transmitted from the Node B.

In step 1304, the UE determines if the recognized number N of OFDMsymbols for ACK/NACK signal transmission is equal to 2.

If it is determined in step 1304 that the number of OFDM symbols forACK/NACK signal transmission is 2, in step 1306, the UE determines withwhich CDM segment set the Node B has transmitted an ACK/NACK signal,among the resource sets for ACK/NACK transmission, defined for N=2. TheUE can determine the CDM segment by detecting the transmission resourcesof the scheduling control information received together with an ACK/NACKsignal, or through signaling from a physical layer and/or upper layer.

When the number of OFDM symbols is 2 and the repetition of each CDMsegment for a corresponding ACK/NACK signal is 3, the UE determines thata CDM segment for a resource set #1 for ACK/NACK transmission is oncemapped to the first OFDM symbol and twice mapped to the second OFDMsymbol. Meanwhile, the UE determines that a resource set #2 for ACK/NACKtransmission twice maps a CDM segment to the first OFDM symbol and oncemaps the CDM segment to the second OFDM symbol.

In step 1308, the UE extracts an ACK/NACK signal from each CDM segmentto which the ACK/NACK signal is mapped, despreads it, combines thedespread ACK/NACK signal with a signal despread after being extractedfrom each CDM segment, and performs decoding thereon.

However, if it is determined in step 1304 that a value of N is not 2, instep 1310, the UE determines with which CDM segment set the Node B hastransmitted an ACK/NACK signal, among the resource sets for ACK/NACKtransmission, defined for N=1 or 3. The UE can determine the CDM segmentby detecting the transmission resources of the scheduling controlinformation received together with an ACK/NACK signal, or throughsignaling from a physical layer and/or upper layer. In step 1312, the UEextracts an ACK/NACK signal from each CDM segment to which the ACK/NACKsignal is mapped, despreads it, combines the despread ACK/NACK signalwith a signal despread after being extracted from each CDM segment, andperforms decoding thereon.

A detailed transmission/reception apparatus of the third embodiment isequal to that of the first embodiment, so a description thereof will beomitted. However, the detailed parameters and methods for mappingresources for ACK/NACK transmission follow the assumptions made in thethird embodiment.

Fourth Embodiment

A fourth embodiment of the present invention is applied to MBSFN servicesupporting broadcast service such as Mobile-TV. The fourth embodimentconsiders the situation in which an ACK/NACK signal is spread with aspreading factor 4 and mapped to a CDM segment, the CDM segment isrepeated 3 times, and the ACK/NACK signal is transmitted during first 2OFDM symbols in a subframe by applying a Space-Frequency Block Coding(SFBC) method, which is a diversity transmission method based on 4transmit antennas. SFBC, a combination of complex conjugation and signreversal for a desired transmission signal, is a technology forobtaining diversity gain by reconfiguring a signal so that it hasorthogonality over a spatial domain and a frequency domain.

With reference to FIGS. 14 and 15, a description will now be made of thedetailed operating principle of mapping an ACK/NACK signal to aplurality of transmit antennas by applying an SFBC method according tothe present invention performed on the above conditions. Forconvenience, only ACK/NACK signals are illustrated, and other UL/DLscheduling information and pilot signals are not illustrated.

An ACK/NACK signal for an arbitrary UE(i) is generated as a modulationsymbol through Binary Phase Shift Keying (BPSK) or Quadrature PhaseShift Keying (QPSK) modulation, and the generated ACK/NACK modulationsymbol is spread with a length-4 orthogonal code and mapped to a CDMsegment. The CDM segment is a resource unit including consecutive REs inthe time-frequency domain, the number of which corresponds to aspreading factor of an orthogonal code for ACK/NACK transmission, andthe REs are excluded, to which other control signals except for pilotsignals (or RSs) for channel estimation and ACK/NACK are mapped. Aphysical channel for transmitting an ACK/NACK signal for the UE(i) isdefined as PHICH(i). PHICHs can be multiplexed to the same CDM segment.The number of PHICHs corresponds to a spreading factor of an orthogonalcode applied for spreading an ACK/NACK signal, and a set of PHICHsmultiplexed to the same CDM segment is defined as a PHICH group.

If I/Q multiplexing of different PHICHs to a real component and animaginary component is applied, a maximum of SF*2 PHICHs can bemultiplexed to the same CDM segment. PHICHs belonging to the same PHICHgroup are multiplexed to the same CDM segment, and repeatedlytransmitted in the frequency domain three times. That is, a size of aCDM segment for transmitting one PHICH is 4 (SF=4), and the PHICH ismapped to 3 different CDM segments in the frequency domain. Forconvenience, each CDM segment is independently expressed with arepetition index r (r=0, 1, . . . , R−1, R=3).

That is, among the CDM segments repeated 3 times in the frequencydomain, the first CDM segment is identified by a repetition index r=0,the second CDM segment is identified by a repetition index r=1, and thethird CDM segment is identified by a repetition index r=2. Additionally,if a PHICH group index g (g=0, 1, . . . G−1) for identifying a PHICHgroup to which PHICH(i) for an arbitrary UE(i) belongs is defined, itcan be calculated as shown in Equation (1).g=floor(i/PHICH_GROUP_SIZE)  (1)

In Equation (1), PHICH_GROUP_SIZE is a value indicating how many PHICHsare CDM-multiplexed to one PHICH group, and it is SF*2 if I/Qmultiplexing is applied. Otherwise, it is SF.

In the present invention, if an ACK/NACK modulation symbol is spreadwith an SF=4 orthogonal code, a signal including four chips a1, a2, a3,and a4 is generated. A pattern for sequentially mapping the generatedchips to a CDM segment of an antenna #0 (1402 of FIG. 14 or 1502 of FIG.15) among 4 transmit antennas in the frequency domain, and sequentiallymapping −a2*, a1*, −a4*, and a3*, which are expressed with complexconjugates or sign-reversed signals of the generated chips, to a CDMsegment of an antenna #2 (1406 or 1506) in the frequency domain, iscalled a pattern A, where a* is a complex conjugate of a.

A pattern for sequentially mapping a1, a2, a3, and a4 generated byspreading an ACK/NACK signal with an SF=4 orthogonal code to a CDMsegment of an antenna #1 (1404 or 1504) among 4 transmit antennas in thefrequency domain, and sequentially mapping −a2*, a1*, −a4*, and a3*,which are expressed with complex conjugates or sign-reversed signals ofthe generated chips, to a CDM segment of an antenna #3 (1408 or 1508) inthe frequency domain, is called a pattern B.

In applying SFBC based on 4 transmit antennas to PHICH for transmittingan ACK/NACK signal spread with the SF=4 orthogonal code, antenna mappingis performed with one of the following two methods according to a PHICHgroup index g and a repetition index r.

FIG. 14 illustrates an example of transmitting PHICH according to arepetition index r of a CDM segment, i.e., transmitting PHICH with apattern A 1410 for r=0, with a pattern B 1412 for r=1, and with apattern A 1414 for r=2. Herein, this process will be referred to as“A-B-A antenna mapping”.

FIG. 15 illustrates an example of transmitting PHICH according to arepetition index r of a CDM segment, i.e., transmitting PHICH with apattern B 1510 for r=0, a pattern A 1512 for r=1, and a pattern. B 1514for r=2. Herein, this process will be referred to as “B-A-B antennamapping”.

By performing A-B-A mapping according to a PHICH group index g, i.e.,for g=even number, and performing B-A-B mapping for g=odd number (or itsinverse operation is also possible), transmit power between antennas isuniformly distributed when a plurality of PHICHs are transmitted,thereby preventing the situation where a particular antenna ispower-overloaded.

FIG. 16 illustrates a method for mapping a PHICH group in atime-frequency domain depending on an antenna mapping method accordingto a preferred embodiment of the present invention.

Referring to FIG. 16, the horizontal axis represents the frequencydomain, and the vertical axis represents the time domain. CDM segmentsincluded in one PHICH group are mapped to different zones in thefrequency domain, and mapped within an OFDM symbol #1 and an OFDM symbol#2 in the time domain in a distributed manner. An index for identifyingan OFDM symbol is denoted by n, where n=0, 1.

The first CDM segment (r=0) of a PHICH group g=0 (1602) is mapped to theOFDM symbol #1 (n=0) by applying the antenna mapping pattern A (1610),the second CDM segment (r=1) is mapped to the OFDM symbol #2 (n=1) byapplying the antenna mapping pattern B (1626), and the third CDM segment(r=2) is mapped to the OFDM symbol #1 (n=0) by applying the antennamapping pattern A (1618). The first CDM segment (r=0) of a PHICH groupg=1 (1604) is mapped to the OFDM symbol #1 (n=0) by applying the antennamapping pattern B (1612), the second CDM segment (r=1) is mapped to theOFDM symbol #2 (n=1) by applying the antenna mapping pattern A (1628),and the third CDM segment (r=2) is mapped to the OFDM symbol #1 (n=0) byapplying the antenna mapping pattern B (1620).

That is, for PHICH group g=0 and PHICH group g=1, their methods formapping each CDM segment to an OFDM symbol in the time domain aremaintained equally, and their antenna mapping patterns are maintaineddifferently as A-B-A mapping and B-A-B mapping, respectively. Therefore,when 2 PHICH groups are mapped and transmitted, transmit power betweenantennas is maximally uniformly distributed at an arbitrary time,thereby preventing the situation where a particular antenna ispower-overloaded.

Additionally, when a PHICH group is transmitted, the first CDM segment(r=0) of a PHICH group g=2 (1606) is mapped to the OFDM symbol #2 (n=1)by applying the antenna mapping pattern A (1622), the second CDM segment(r=1) is mapped to the OFDM symbol #1 (n=0) by applying antenna mappingpattern B (1614), and the third CDM segment (r=2) is mapped to the OFDMsymbol #2 (n=1) by applying the antenna mapping pattern A (1630). Thefirst CDM segment (r=0) of a PHICH group g=3 (1608) is mapped to theOFDM symbol #2 (n=1) by applying the antenna mapping pattern B (1624),the second CDM segment (r=1) is mapped to the OFDM symbol #1 (n=0) byapplying the antenna mapping pattern A (1616), and the third CDM segment(r=2) is mapped to the OFDM symbol #2 (n=1) by applying the antennamapping pattern B (1632).

That is, for PHICH group g=2 and PHICH group g=3, their methods formapping each CDM segment to an OFDM symbol in the time domain aremaintained equally, and their antenna mapping patterns are maintaineddifferently as A-B-A mapping and B-A-B mapping, respectively. Therefore,when a total of 4 PHICH groups are mapped and transmitted, transmitpower between antennas is maximally uniformly distributed at anarbitrary time and at the same time, transmit power between OFDM symbolsis also maximally uniformly distributed, thereby preventing thesituation where particular antenna and OFDM symbol are power-overloaded.

The complexity of a mapping operation can be reduced by matching afrequency-domain location of each CDM segment in PHICH group g=2 andPHICH group g=3 to the predetermined frequency-domain location of eachCDM segment of PHICH group g=0 and PHICH group g=1.

If there is a need to map and transmit more than a total of 4 PHICHgroups, the added PHICH group(s) applies the mapping operation definedfor PHICH groups g=0-3 so that the PHICH groups do not overlap eachother in the time-frequency domain.

The mapping operations described in conjunction with FIGS. 14 and 15 canbe summarized as shown in Table 1.

TABLE 1 CDM segment OFDM symbol Antenna mapping PHICH group g repetitionindex r index n pattern 0 0 0 A 0 1 1 B 0 2 0 A 1 0 0 B 1 1 1 A 1 2 0 B2 0 1 A 2 1 0 B 2 2 1 A 3 0 1 B 3 1 0 A 3 2 1 B . . . . . . . . . . . .

In Table 1, when the first CDM segment r=0 of a PHICH group g=0 ismapped to an OFDM symbol n=0 (when a start symbol of an OFDM symbol isdefined as n=0), an OFDM symbol index n is mapped in order of [010, 010,101, 101, . . . ]. When the first CDM segment r=0 of the PHICH group g=0is mapped beginning at an OFDM symbol n=1 (when a start symbol of anOFDM symbol is defined as n=1), an OFDM symbol index n is mapped inreversed order of [101, 101, 010, 010 . . . ].

As described above, information indicating which CDM segments the UEshould monitor in order to receive the ACK/NACK signal from a Node B isimplicitly notified by a mapping relation with scheduling controlinformation or resources for UL data transmission without separatesignaling, or notified by separate physical layer or upper layersignaling.

A detailed transmission/reception apparatus of the fourth embodiment isto the same as that of the first embodiment, so a description thereofwill be omitted. However, the detailed parameters and methods formapping resources for ACK/NACK transmission follow the assumptions madein the fourth embodiment.

Fifth Embodiment

A fifth embodiment of the present invention is applied to MBSFN servicesupporting broadcast service such as Mobile-TV. The fifth embodimentconsiders a situation in which an ACK/NACK signal is spread with aspreading factor 2 and mapped to a length-2 mini CDM segment, the miniCDM segment is repeated 3 times, and the ACK/NACK signal is transmittedduring first 2 OFDM symbols in a subframe by applying an SFBC method,which is a diversity transmission method based on 4 transmit antennas.

With reference to FIGS. 17 and 18, a description will now be made of thedetailed operating principle of mapping an ACK/NACK signal to aplurality of transmit antennas by applying an SFBC method according tothe present invention performed on the above conditions. Forconvenience, only ACK/NACK signals are shown, and other UL/DL schedulinginformation and pilot signals are not shown.

An ACK/NACK signal for an arbitrary UE(i) is generated as a modulationsymbol through BPSK or QPSK modulation, and the generated ACK/NACKmodulation symbol is spread with a length-2 orthogonal code and mappedto a mini CDM segment. The mini CDM segment is a resource unit includingconsecutive REs in the time-frequency domain, the number of whichcorresponds to a spreading factor of an orthogonal code for ACK/NACKtransmission, and the REs are excluded, to which other control signalsexcept for pilot signals (or RSs) for channel estimation and ACK/NACKare mapped. The 2 mini CDM segments are included in the CDM segmentdescribed in the fourth embodiment. A set of PHICHs multiplexed to thesame mini CDM segment is referred to as a “PHICH group”.

PHICHs belonging to the same PHICH group are multiplexed to the samemini CDM segment, and repeatedly transmitted in the frequency domainthree times. That is, a size of a mini CDM segment for transmitting onePHICH is 2 (SF=2), and the PHICH is mapped to 3 different mini CDMsegments in the frequency domain. For convenience, each mini CDM segmentis independently expressed with a repetition index r (r=0, 1, . . . ,R−1; R=3).

That is, among the mini CDM segments repeated 3 times in the frequencydomain, the first mini CDM segment is identified by a repetition indexr=0, the second mini CDM segment is identified by a repetition indexr=1, and the third mini CDM segment is identified by a repetition indexAdditionally, if a PHICH group index g (g=0, 1, . . . G−1) foridentifying a PHICH group to which PHICH(i) for an arbitrary UE(i)belongs is defined, it can be calculated as shown in Equation (2).g=floor(i/PHICH_GROUP_SIZE)  (2)

In Equation (2), PHICH_GROUP_SIZE is a value indicating how many PHICHsare CDM-multiplexed to one PHICH group, and it is SF*2 if I/Qmultiplexing is applied. Otherwise, it is SF.

In the fifth embodiment, if an ACK/NACK modulation symbol is spread withan SF=2 orthogonal code, a signal including two chips a1 and a2 isgenerated. A pattern for sequentially mapping the generated chips to aCDM segment of an antenna #0 (1702 of FIG. 17 or 1802 of FIG. 18) among4 transmit antennas at the locations M (1716 and 1732 in FIGS. 17, and1824 in FIG. 18) and f1 (1718 and 1734 in FIGS. 17, and 1826 in FIG. 18)in the frequency domain, and sequentially mapping −a2* and a1*, whichare expressed with complex conjugates or sign-reversed signals of thegenerated chips, to a CDM segment of an antenna #2 (1706 or 1806) at thelocations f0 (1716 and 1732 in FIGS. 17, and 1824 in FIG. 18) and f1(1718 and 1734 in FIGS. 17, and 1826 in FIG. 18) in the frequencydomain, and if another ACK/NACK modulation symbol is spread with an SF=2orthogonal code, mapping the generated two chips a1 and a2 to thelocations f2 (1720 and 1736 in FIGS. 17, and 1828 in FIGS. 18) and f3(1722 and 1738 in FIGS. 17, and 1830 in FIG. 18) in the frequencydomain, and mapping −a2* and a1*, which are expressed with complexconjugates or sign-reversed signals of the generated chips, to thelocations f0 and f1 and the locations f2 and f3 of the antenna #2, isreferred to as “pattern A′”.

A pattern for sequentially mapping a1 and a2 generated by spreading anACK/NACK modulation symbol with an SF=2 orthogonal code to a CDM segmentof an antenna #1 (1704 or 1804) among 4 transmit antennas at thelocations f0 and f1 in the frequency domain, and sequentially mapping−a2* and a1*, which are expressed with complex conjugates orsign-reversed signals of the generated chips, to a CDM segment of anantenna #3 (1708 or 1808) at the locations f0 and f1 in the frequencydomain, and if another ACK/NACK modulation symbol is spread with an SF=2orthogonal code, sequentially mapping the generated a1 and a2 to a CDMsegment of the antenna #1(1704 or 1804) among 4 transmit antennas at thelocations f2 and f3 in the frequency domain, and sequentially mapping−a2* and a1*, which are expressed with complex conjugates orsign-reversed signals of the generated chips, to a CDM segment of theantenna #3 (1708 or 1808) at the locations f2 and f3 in the frequencydomain, is referred to as “pattern B′”.

In applying SFBC based on 4 transmit antennas to PHICH for transmittingan ACK/NACK signal spread with the SF=2 orthogonal code, antenna mappingis performed using one of the following two methods according to a PHICHgroup index g and a repetition index r.

FIG. 17 illustrates an example of transmitting PHICH according to arepetition index r of a mini CDM segment, i.e., transmitting PHICH witha pattern A′ 1710 for r=0, with a pattern B′ 1712 for r=1, and with apattern A′ 1714 for r=2. Herein, this will be referred to as “A′-B′-A′antenna mapping”.

FIG. 18 illustrates an example of transmitting PHICH according to arepetition index r of a mini CDM segment, i.e., transmitting PHICH witha pattern B′ 1810 for r=0, with a pattern A′ 1812 for r=1, and with apattern B′ 1814 for r=2. Herein, this will be referred to as “B′-A′-B′antenna mapping”.

By defining an operation of performing A′-B′-A′ mapping according to aPHICH group index g, i.e., for floor(g/2)=even number, and performingmapping for floor(g/2) odd number (or its inverse operation is alsopossible), transmit power between antennas is uniformly distributed whena plurality of PHICHs are transmitted, thereby preventing the situationwhere a particular antenna is power-overloaded.

FIG. 19 is a diagram illustrating a method for mapping a PHICH group ina time-frequency domain depending on an antenna mapping method accordingto the present invention. With reference to FIG. 19, a description willnow be made of a mapping method for uniformly distributing transmitpower between OFDM symbols and antennas to which a PHICH group ismapped.

Referring to FIG. 19, the horizontal axis represents the frequencydomain, and the vertical axis represents the time domain. Mini CDMsegments included in one PHICH group are mapped to different zones inthe frequency domain, and mapped within an OFDM symbol #1 and an OFDMsymbol #2 in the time domain in a distributed manner. An index foridentifying an OFDM symbol is denoted by n, where n=0, 1.

The first mini CDM segment (r=0) of a PHICH group g=0 (1902) is mappedto the OFDM symbol #1 (n=0) by applying the antenna mapping pattern A′(1918), the second mini CDM segment (r=1) is mapped to the OFDM symbol#2 (n=1) by applying the antenna mapping pattern B′ (1950), and thethird mini CDM segment (r=2) is mapped to the OFDM symbol #1 (n=0) byapplying the antenna mapping pattern A′ (1934).

The first mini CDM segment (r=0) of a PHICH group g=1 (1904) is mappedto the OFDM symbol #1 (n=0) by applying the antenna mapping pattern A′(1920), the second mini CDM segment (r=1) is mapped to the OFDM symbol#2 (n=1) by applying the antenna mapping pattern B′ (1952), and thethird mini CDM segment (r=2) is mapped to the OFDM symbol #1 (n=0) byapplying the antenna mapping pattern A′ (1936).

The first mini CDM segment (r=0) of a PHICH group g=2 (1906) is mappedto the OFDM symbol #1 (n=0) by applying the antenna mapping pattern B′(1922), the second mini CDM segment (r=1) is mapped to the OFDM symbol#2 (n=1) by applying the antenna mapping pattern A′ (1954), and thethird mini CDM segment (r=2) is mapped to the OFDM symbol #1 (n=0) byapplying the antenna mapping pattern B′ (1938).

The first mini CDM segment (r=0) of a PHICH group g=3 (1908) is mappedto the OFDM symbol #1 (n=0) by applying the antenna mapping pattern B′(1924), the second mini CDM segment (r=1) is mapped to the OFDM symbol#2 (n=1) by applying the antenna mapping pattern A′ (1956), and thethird mini CDM segment (r=2) is mapped to the OFDM symbol #1 (n=0) byapplying the antenna mapping pattern B′ (1940).

That is, for PHICH groups g=0-3, their methods for mapping each mini CDMsegment to an OFDM symbol in the time domain are maintained equally, andthe antenna mapping pattern applies the A′-B′-A′ mapping for PHICH groupg=0-1 and the B′-A′-B′ mapping for PHICH group g=2-3. Therefore, when 4PHICH groups are mapped and transmitted, transmit power between antennasis maximally uniformly distributed at an arbitrary time, therebypreventing the situation where a particular antenna is power-overloaded.

Additionally, when a PHICH group is transmitted, the first mini CDMsegment (r=0) of a PHICH group g=4 (1910) is mapped to the OFDM symbol#2 (n=1) by applying the antenna mapping pattern A′ (1942), the secondmini CDM segment (r=1) is mapped to the OFDM symbol #1 (n=0) by applyingthe antenna mapping pattern B′ (1926), and the third mini CDM segment(r=2) is mapped to the OFDM symbol #2 (n=1) by applying antenna mappingpattern A′ (1958).

The first mini CDM segment (r=0) of a PHICH group g=5 (1912) is mappedto the OFDM symbol #2 (n=1) by applying the antenna mapping pattern A′(1944), the second mini CDM segment (r=1) is mapped to the OFDM symbol#1 (n=0) by applying the antenna mapping pattern B′ (1928), and thethird mini CDM segment (r=2) is mapped to the OFDM symbol #2 (n=1) byapplying the antenna mapping pattern A′ (1960).

The first mini CDM segment (r=0) of a PHICH group g=6 (1914) is mappedto the OFDM symbol #2 (n=1) by applying the antenna mapping pattern B′(1946), the second mini CDM segment (r=1) is mapped to the OFDM symbol#1 (n=0) by applying the antenna mapping pattern A′ (1930), and thethird mini CDM segment (r=2) is mapped to the OFDM symbol #2 (n=1) byapplying the antenna mapping pattern B′ (1962).

The first mini CDM segment (r=0) of a PHICH group g=7 (1916) is mappedto the OFDM symbol #2 (n=1) by applying the antenna mapping pattern B′(1948), the second mini CDM segment (r=1) is mapped to the OFDM symbol#1 (n=0) by applying the antenna mapping pattern A′ (1932), and thethird mini CDM segment (r=2) is mapped to the OFDM symbol #2 (n=1) byapplying the antenna mapping pattern B′ (1964).

That is, for PHICH groups g=4-7, their methods for mapping each mini CDMsegment to an OFDM symbol in the time domain are maintained equally, andthe antenna mapping pattern applies the A′-B′-A′ mapping for PHICH groupg=4-5 and the B′-A′-B′ mapping for PHICH group g=6-7. Therefore, when atotal of 8 PHICH groups are mapped and transmitted, transmit powerbetween antennas is maximally uniformly distributed at an arbitrary timeand at the same time, transmit power between OFDM symbols is alsomaximally uniformly distributed, thereby preventing the situation wherea particular antenna and OFDM symbol are power-overloaded.

The complexity of a mapping operation can be reduced by matching afrequency-domain location of each CDM segment in PHICH group g=4-7 tothe predetermined frequency-domain location of each CDM segment of PHICHgroup g=0-3.

If there is a need to map and transmit more than a total of 8 PHICHgroups, the added PHICH group(s) applies the mapping operation definedfor PHICH groups g=0-7 so that the PHICH groups do not overlap eachother in the time-frequency domain.

The mapping operation described in conjunction with FIGS. 17 and 18 canbe summarized as shown in Table 2.

TABLE 2 Mini CDM segment OFDM symbol Antenna mapping PHICH group grepetition index r index n pattern 0 0 0 A′ 0 1 1 B′ 0 2 0 A′ 1 0 0 A′ 11 1 B′ 1 2 0 A′ 2 0 0 B′ 2 1 1 A′ 2 2 0 B′ 3 0 0 B′ 3 1 1 A′ 3 2 0 B′ 40 1 A′ 4 1 0 B′ 4 2 1 A′ 5 0 1 A′ 5 1 0 B′ 5 2 1 A′ 6 0 1 B′ 6 1 0 A′ 62 1 B′ 7 0 1 B′ 7 1 0 A′ 7 2 1 B′ . . . . . . . . . . . .

In Table 2, when the first CDM segment r=0 of a PHICH group g=0 ismapped to an OFDM symbol n=0 (when a start symbol of an OFDM symbol isdefined as n=0), an OFDM symbol index n is mapped in order of [010, 010,010, 010, 101, 101, 101, 101, . . . ]. When the first CDM segment r=0 ofthe PHICH group g=0 is mapped beginning at an OFDM symbol n=1 (when astart symbol of an OFDM symbol is defined as n=1), an OFDM symbol indexn is mapped in reversed order of [101, 101, 101, 101, 010, 010, 010, 010. . . ].

Information indicating which CDM segments the UE should monitor in orderto receive the ACK/NACK signal from a Node B is implicitly notified by amapping relation with scheduling control information or resources for ULdata transmission without separate signaling, or notified by separatephysical layer or upper layer signaling.

A detailed transmission/reception apparatus of the fifth embodiment isequal to that of the first embodiment, so a description thereof will beomitted. However, the detailed parameters and methods for mappingresources for ACK/NACK transmission follow the assumptions made in thefifth embodiment.

Sixth Embodiment

A sixth embodiment of the present invention is applied to MBSFN servicesupporting broadcast service such as Mobile-TV. The sixth embodimentconsiders a situation in which an ACK/NACK signal is spread with aspreading factor 4 and mapped to a CDM segment, the CDM segment isrepeated 3 times, and the ACK/NACK signal is transmitted during first 2OFDM symbols in a subframe by applying an SFBC method which is adiversity transmission method based on 4 transmit antennas.

The sixth embodiment, another modification of the fourth embodiment, towhich the antenna mapping patterns A and B defined in the fourthembodiment are applied, maps PHICH groups in the time-frequency domainas illustrated in FIG. 18.

Referring to FIG. 20, the horizontal axis represents the frequencydomain, and the vertical axis represents the time domain. CDM segmentsincluded in one PHICH group are mapped to different zones in thefrequency domain, and mapped within the OFDM symbol #1 and the OFDMsymbol #2 in the time domain in a distributed manner. An index foridentifying an OFDM symbol is denoted by n, where n=0, 1.

The first CDM segment (r=0) of a PHICH group g=0 (2002) is mapped to theOFDM symbol #1 (n=0) by applying the antenna mapping pattern A (2006),the second CDM segment (r=1) is mapped to the OFDM symbol #2 (n=1) byapplying the antenna mapping pattern B (2014), and the third CDM segment(r=2) is mapped to the OFDM symbol #1 (n=0) by applying the antennamapping pattern A (2010).

The first CDM segment (r=0) of a PHICH group g=1 (2004) is mapped to theOFDM symbol #2 (n=1) by applying the antenna mapping pattern A (2012),the second CDM segment (r=1) is mapped to the OFDM symbol #1 (n=0) byapplying the antenna mapping pattern B (2008), and the third CDM segment(r=2) is mapped to the OFDM symbol #2 (n=1) by applying the antennamapping pattern A (2016).

That is, for PHICH group g=0 and PHICH group g=1, their antenna mappingpatterns for CDM segments are equally maintained as the A-B-A mapping(or B-A-B mapping), and their methods for mapping each CDM segment to anOFDM symbol in the time domain are maintained differently. Therefore,when 2 PHICH groups are mapped and transmitted, transmit power betweenantennas is uniformly distributed to some extent at an arbitrary time,and transmit power between OFDM symbols is maximally uniformlydistributed.

The complexity of a mapping operation can be reduced by matching afrequency-domain location of each CDM segment in PHICH group g=1 to thepredetermined frequency-domain location of each CDM segment of PHICHgroup g=0.

If there is a need to map and transmit more than a total of 2 PHICHgroups, the added PHICH group(s) applies the mapping operation definedfor PHICH groups g=0-1 so that the PHICH groups do not overlap eachother in the time-frequency domain.

The foregoing mapping operation can be summarized as shown Table 3.

TABLE 3 CDM segment OFDM symbol Antenna mapping PHICH group g repetitionindex r index n pattern 0 0 0 A 0 1 1 B 0 2 0 A 1 0 1 A 1 1 0 B 1 2 1 A. . . . . . . . . . . .

In Table 3, when the first CDM segment r=0 of a PHICH group g=0 ismapped to an OFDM symbol n=0 (when a start symbol of an OFDM symbol isdefined as n=0), an OFDM symbol index n is mapped in order of [010, 101,. . . ]. When the first CDM segment r=0 of the PHICH group g=0 is mappedbeginning at an OFDM symbol n=1 (when a start symbol of an OFDM symbolis defined as n=1), an OFDM symbol index n is mapped in reversed orderof [101, 010, . . . ].

Information indicating which CDM segments the UE should monitor in orderto receive the ACK/NACK signal from a Node B is implicitly notified by amapping relation with scheduling control information or resources for ULdata transmission without separate signaling, or notified by separatephysical layer or upper layer signaling.

A detailed transmission/reception apparatus of the sixth embodiment isto the same as that of the first embodiment, so a description thereofwill be omitted. However, the detailed parameters and methods formapping resources for ACK/NACK transmission follow the assumptions madein the sixth embodiment. The sixth embodiment is similar to the fourthembodiment, however, in which the number of PHICH groups is 2.

In the PHICH mapping methods of the fourth and fifth embodiments, themapping rules in the time-frequency domain can be mathematicallygeneralized as expressed in Equation (3).

For mapping of PHICH belonging to a PHICH group g, an indexA₀(g,r)=A₀(g,0), A₀(g,1), . . . , A₀(g,R−1) of a dummy CDM segment isdetermined such that it is located in the first OFDM symbol. Here, r(r=0, 1 . . . R−1) indicates a repetition index of a CDM segment. Basedon the number, N (n=0, 1, . . . , N−1), of OFDM symbols on which PHICHis transmitted, the PHICH group index g, and the repetition index r of aCDM segment, the CDM segment to which PHICH is actually mapped becomesA(g,r)=A(g,0), A(g,1), . . . , A(g,R−1), and A(g,r) is calculated asEquation (3).A(g,r)=A ₀(g,r)+mod(floor(g/K),N)  (3)

Here, K=2 for N=2, SF=4, and number of transmit antennas=4; K=4 for N=2,SF=2, and number of transmit antenna=4; and otherwise, K=1.

In Equation (3), mod(a, b) is a remainder obtained by dividing a by b.

For example, when this scheme is used, the operation illustrated in FIG.16 is performed for K=2, and the operation of FIG. 19 is performed forK=4.

As is apparent from the foregoing description, the present inventiontransmits an HARQ ACK/NACK signal through at least one OFDM symbol in adistributed manner considering a predetermined repetition, therebysatisfying HARQ reliability. That is, in transmitting/receiving the HARQACK/NACK signal, the present invention obtains diversity gain against aninterference signal, maintains orthogonality between multiplexedorthogonal signals, and provides diversity gain in the time-frequencydomain. In addition, the present invention prevents the case where aparticular OFDM symbol is power-overloaded, thereby contributing toimprovement of the entire system performance of the mobile communicationsystem supporting HARQ.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

What is claimed is:
 1. A method for mapping resource elements to amultiple antenna array to transmit control information in a mobilecommunication system, comprising: spreading the control information to aplurality of resource elements according to a spreading factor; andmapping the resource elements to the multiple antenna array based on arepetition index, wherein the resource elements are mapped to themultiple antenna array in an alternating pattern in accordance with therepetition index.
 2. The method of claim 1, wherein at least one ofcomplex conjugation and sign reversal is applied to map the resourceelements to the multiple antenna array.
 3. The method of claim 1,wherein the repetition index is three (3).
 4. The method of claim 3,wherein the multiple antenna array includes four (4) antennas and thespreading factor is four (4).
 5. The method of claim 1, wherein theresource elements include four (4) consecutive resource elementscorresponding to the spreading factor for Acknowledge/NegativeAcknowledge (ACK/NACK) transmission, in a time-frequency domain.
 6. Themethod of claim 1, wherein if a start symbol of an Orthogonal FrequencyDivision Multiplexing (OFDM) symbol is defined as n=0, a symbol index nfor the transmission of the control information is mapped in thefollowing order: [010, 010, 101, 101, . . . ].
 7. The method of claim 1,wherein if a start symbol of an Orthogonal Frequency DivisionMultiplexing (OFDM) symbol is defined as n=1, a symbol index n for thetransmission of the control information is mapped in the followingorder: [101, 101, 010, 010 . . . ].
 8. The method of claim 1, whereinthe alternating pattern is applied between at least two Physical HybridAutomatic Repeat reQuest (HARQ) Indicator Channel (PI-ICH) groups amonga plurality of PHICH groups.
 9. The method of claim 1, wherein theresource elements are mapped to the multiple antenna array according tothe following table: Antenna PHICH Repetition Symbol Mapping Group gIndex r Index n Pattern 0 0 0 A 0 1 1 B 0 2 0 A 1 0 0 B 1 1 1 A 1 2 0 B2 0 1 A 2 1 0 B 2 2 1 A 3 0 1 B 3 1 0 A 3 2 1 B . . . . . . . . . . . . .


10. An apparatus for mapping resource elements to a multiple antennaarray to transmit control information in a mobile communication system,comprising: a processor that spreads the control information to aplurality of resource elements according to a spreading factor and mapsthe resource elements to the multiple antenna array based on arepetition index, wherein the resource elements are mapped to themultiple antenna array in an alternating pattern in accordance with therepetition index.
 11. The apparatus of claim 10, wherein at least one ofcomplex conjugation and sign reversal is applied to map the resourceelements to the multiple antenna array.
 12. The apparatus of claim 10,wherein the repetition index is three (3).
 13. The apparatus of claim12, wherein the multiple antenna array includes four (4) antennas andthe spreading factor is four (4).
 14. The apparatus of claim 10, whereinthe resource elements include four (4) consecutive resource elementscorresponding to the spreading factor for Acknowledge/NegativeAcknowledge (ACK/NACK) transmission, in a time-frequency domain.
 15. Theapparatus of claim 10, wherein if a start symbol of an OFDM symbol isdefined as n=0, a symbol index n for the transmission of the controlinformation is mapped in the following order: [010, 010, 101, 101, . . .].
 16. The apparatus of claim 10, wherein if a start symbol of an OFDMsymbol is defined as n=1, a symbol index n for the transmission of thecontrol information is mapped in the following order: [101, 101, 010,010 . . . ].
 17. The apparatus of claim 10, wherein the alternatingpattern is applied between at least two Physical Hybrid Automatic RepeatreQuest (HARQ) Indicator Channel (PHICH) groups among a plurality ofPHICH groups.
 18. The apparatus of claim 10, wherein the resourceelements are mapped to the multiple antenna array according to thefollowing table: Antenna PHICH Repetition Symbol Mapping Group g Index rIndex n Pattern 0 0 0 A 0 1 1 B 0 2 0 A 1 0 0 B 1 1 1 A 1 2 0 B 2 0 1 A2 1 0 B 2 2 1 A 3 0 1 B 3 1 0 A 3 2 1 B . . . . . . . . . . . .  .